Effect of hydroseeding on grass yield and water use efficiency on forest road artificial soil slopes

JOURNAL OF FOREST SCIENCE, 64, 2018 (4): 157–163

https://doi.org/10.17221/2/2018-JFS

Effect of hydroseeding on grass yield and water use

efficiency on forest road artificial soil slopes

Aidin PARSAKHOO

_{*, Mohammad JAJOUZADEH}

_{, Ayoob REZAEE MOTLAGH}

1 _{Department of Forestry, Faculty of Forest Science,}

Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran

2 _{Department of Silviculture and Forest Ecology, Faculty of Forest Science,}

Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran *Corresponding author: Aidinparsakhoo@yahoo.com

Abstract

Parsakhoo A., Jajouzadeh M., Rezaee Motlagh A. (2018): Effect of hydroseeding on grass yield and water use efficiency on forest road artificial soil slopes. J. For. Sci., 64: 157–163.

Hydroseeding treatments are increasingly being used as a feasible alternative for soil erosion control after forest road construction. This study investigated the germination and biomass production of two hydroseed mixes and assessed the effectiveness of these treatments to reduce the water consumption of grass. Hydroseed mix 1 (water + seed + or-ganic tackifier + starter fertilizer + superabsorbent) and hydroseed mix 2 (mentioned materials in mix 1 + biohumus + cellulose fibre mulch + natural yarn) were compared to a control (prevalent mix including seed + animal fertilizer) during the study period (30 days in July). Hydroseed mix 2 significantly favoured both seed germination parameters and grass biomass production. Hydroseed mix 2 significantly reduced the quantity of irrigation watervia producing an absorbent layer. The results from this study could help managers to select and apply more appropriate hydroseeding treatments for slope stabilization of forest road embankments.

Keywords: hydroseed mixes; grass germination; fibre mulch; stabilization; consumption

Created artificial slopes during the topographic change by road construction are susceptible to wa-ter erosion and are commonly stabilized by reveg-etation (Wagenbrenner et al. 2006; Rivera et al. 2014). Different effective road slope stabilization methods such as hydroseeding, topsoil spreading, geotextile installation and planting have been de-veloped and used around the world (Akbarzadeh et al. 2009; Rivera et al. 2014). Over the past de-cade, the use of hydroseeded grasses has greatly increased because of their restoration and habitat advantages as well as their beauty (Marques et al. 2007; Rivera et al. 2014).

Some grasses can reduce runoff and sediment concentrations by 65–70 and 80–95%, respectively (Li et al. 2011). Their cover also consists of numer-ous grass stems that enhance the trap sediment

and slow down surface runoff. Grasses are also capable of forming root mats in the soil that act as mechanical barriers to sediment loss (Gyasi-Agyei 2004; Fox et al. 2010). Plant roots signifi-cantly affect soil erosion (Pan, Shangguan 2006). The establishment of grass will require a detailed analysis of the site in terms of access to irriga-tion water, established weeds and other ground covers as well as soil erosion process (Babcock, McLaughlin 2011).

been applied on soil slopes by hydroseeding or oth-er techniques (Liu et al. 2010). Hydroseeding is an important and popular treatment to stabilize steep slopes (Adekalu et al. 2007). A hydroseed binder can decrease sediment production by providing cover on bare soil, reducing raindrop impact ero-sion, reducing runoff during precipitation events by increasing infiltration into the soil and increas-ing soil water-holdincreas-ing capacity by decreasincreas-ing soil evaporation (Albaladejo Montoro et al. 2000; Groen, Woods 2008).

Hydroseeding is a process by which seed, water, fertilizer, and sometimes fibre mulch and binders are blended together in a tank and applied onto bare soil surfaces through hydroseeder equip-ment (Wagenbrenner et al. 2006; Dodson, Peterson 2009). When sprayed, the cellulose fi-bre mulch together with fertilizer and grass seed will act as an absorbent mat, holding enough moisture to allow the proper and rapid germina-tion of grass seeds and at the same time forming a cover to prevent soil erosion (Faucette et al. 2004; Holt et al. 2005; Babcock, McLaughlin 2013). However, information regarding the effec-tiveness of these techniques in erosion control, ir-rigation requirement and vegetative parameters of grasses is scarce (Enriquez et al. 2004; Dodson, Peterson 2009). Hydroseeding can achieve dense grass cover in the short term by stabiliz-ing the soil, thus controllstabiliz-ing erosion (Robichaud et al. 2000). This technique was widely used for grass establishment on road cuts and fills (Muzzi et al. 1997; Bochet, García-Fayos 2004). Grass rapidly develops a fine, extensive root system that stabilizes soil particles. In this study a grass spe-cies (Poa annua Linnaeus) was used to establish steep slopes. The objectives of this study were to examine the vegetative parameters of grass asso-ciated with different mixtures, and assess the ef-fects of hydroseed mixes on water requirements for irrigation.

MATERIAL AND METHODS

The study site was located in the forest engineer-ing laboratory at the Gorgan University of Agricul-tural Sciences and NaAgricul-tural Resources (36°50'32"N and 54°26'22"E) in the Golestan Province, Iran. The experiments were conducted in July 2017 on artificial soil slopes with obvious bare and eroded surfaces. Climate records as measured at a Gor-gan weather station show that the mean annual air temperature during the study was 32°C, with a maximum daily temperature of 39°C for the hot-test day, and a daily minimum of 27°C for the cold-est day (Mohammadi et al. 2017). The soil texture was clay (14% sands, 40% silts, 46% clays). Soil bulk density was 1.2 g·cm–3 _{with a pH of 7.7. Hydroseed} binders in this study were produced based on the native materials and hydroseeding Protocol Op-tions. To establish these binders, it is important to prepare the site and remove weeds. The site must be cleared of trash to ensure maximum contact of the hydroseed slurry to the soil. Formulations ap-plied to produce seed mixes are shown in Table 1.

Grass (P. annua) seeds are enclosed by sets of bracts, called the lemma and the palea. These struc-tures provide a protective covering and are believed to reduce seed breakage during seeding agitation and application. Organic tackifiers are sticking agents that bind soil particles together and protect the surface from wind and water erosion. They are derived from plant materials which include natural polysaccharide (ionic starch) and agar. Seed Starter Fertilizer 20-20-20 formulation (fortified amino acids + gibberellic acid + microelements) is ideal for hydroseeding (Babcock, McLaughlin 2013). Adding a fertilizer to the slurry can reduce germi-nation of certain species due to the effects of fer-tilizer salts on seed imbibition, or uptake of water. This is not just a problem when seeds and fertil-izers are mixed together in the slurry tank; it can also negatively impact the seeds after they are

ap-Table 1. Formulation of seed mixtures used in soil erosion control experiments

Hydroseed mix 1 Hydroseed mix 2 Prevalent mix

Water (l) 5 5 5

Seed (g) 30 30 30

Organic tackifier (g) 20 20 0

Starter fertilizer (g) 30 30 0

Biohumus (g) 0 30 0

Cellulose fibre mulch (g) 0 100 0

Superabsorbent (g) 10 10 0

Natural yarn (g) 0 10 0

plied to the soil surface and before the first rains di-lute the surrounding salts. Effects of fertilizer salts will be more detrimental on sites with low rainfall. Cellulose fibre mulch (saw dust) together with the biohumus will act as an absorbent mat, holding enough moisture to allow the proper germination of grass seeds. Natural yarn will hold materials together as a sheet and is referred to as a bonded matrix. The length of the yarn is an important char-acteristic in creating a matrix sheet. The length of goat yarn in this study was 2 cm. Seed that is sown on the surface and pressed into the soil increases germination rates over broadcast sowing. Seeds are dropped from a seeder mounted in front of the im-printer and then pressed into the soil (Fig. 1).

Experimental design. The erosion control treat-ments examined in the present study are: (i) hy-droseed mix 1, (ii) hydroseed mix 2, (iii) prevalent mix. Treatments were conducted in 5 replications on artificial soil slopes (soil boxes). The soil box had variable slopes (20, 45 and 70°) with dimensions of 0.40 m length, 0.2 m depth and 0.25 m width (Fig. 2). The bottom of the soil box was filled with 10 cm of sand covered with a layer of gauze to keep the water drainage conditions close to those of the test soil; thus, water can easily infiltrate into the soil during the test. Irrigation was carried out once or twice per day after sunset for as long as it takes the surface soil to start to glisten. Most grasses will germinate in 5 to 10 days at optimal temperatures. The experimental design consisted of randomized blocks with 3 × 3 factorial arrangement and five replications. Totally 45 soil boxes or samples were

used in this study. Fig. 1. Erosion control treatments used in the present study: hydroseed mix 1 (a), hydroseed mix 2 (b), prevalent mix (c)

Fig. 2. The test condition and boxes in an open-top laboratory (a)

(b)

Grass biomass and irrigation quantity mea-surements. Seed germination in each soil box was observed daily and the germinated seeds were counted. Seeds were considered germinated when the radicle was 5 mm long (Sosa et al. 2005). Final germination percentage (FG) and mean daily ger-mination (MDG) were calculated by Eqs 1 and 2 (Hossain et al. 2005; Li et al. 2006):

FG _Nn100 (1)

where:

n – number of germinated seeds,

N – total number of seeds.

FG MDG

D

 (2)

where:

D – number of days to final germination percentage. To assess the germination rate (GR), the mean germination time was calculated by Eq. 3:

1

GR n i

i i

n t







where:

n_i – number of germinated seeds in day t_i.

Germination index (GI) and seedling vitality (V) were calculated by Eqs 4 and 5 (Karaguzel et al. 2004; Hossain et al. 2005):

GI t ni i

N



 (4)

FW DW 100_FW

V    (5)

where:

FW – seedling fresh weight, DW – seedling dry weight.

The experiment was concluded after 30 days and various growth indices such as root and stem length, stem fresh weight, root fresh weight, stem dry weight and root dry weight were measured (Baskin et al. 2004; Phartyal et al. 2005). Dry weight was determined after drying the seedlings in an oven at 80°C for 24 h. Then, seedling weight was measured by digital balance to the nearest mg. At the end of the month, the consumed water of irrigations was estimated (Faucette et al. 2004).

Statistical analysis. Statistical analyses were conducted using SPSS (Version 13.0, 2005). To test whether the differences between the treatments were statistically significant (P < 0.05), one-way ANOVA and Duncan’s multiple comparison

proce-dure were performed on germination parameters, biomass production, runoff and soil erosion.

RESULTS AND DISCUSSION

In this study, germination parameters were sig-nificantly related to seeding treatments for erosion control (P < 0.0001). MDG was significantly and negatively related to the slope angle of plots (P = 0.043). There was no significant statistical difference in other germination parameters between the slope treatments (P > 0.05). Treatment types had a signifi-cant effect on the grass biomass production. There were no significant differences in grass biomass pro-duction between the slope treatments except for the total length and total fresh weight of grass (P < 0.05). The irrigation volume of grass in hydroseed mix 2 was significantly different from the other two treat-ments (P < 0.0001, in both cases) (Table 2).

Germination parameters of grass

Germination parameters of hydroseed mix 2 dur-ing the 30 days of study were higher than those of other treatments, particularly in the slope of 20°. MDG and GR in response to the hydroseed mix treatments were significantly faster than in response to the prevalent mix type. Starter fertilizer acceler-ated the germination of grass. At the end of the study GI varied from 1.78–3.22 in the prevalent mix plots to 6.00–7.60 in the hydroseed mix plots (Table 3). The reason for the low GI of prevalent mix was that the surface of grass seeds had not been covered by a soft layer of organic fertilizer immediately after seeding (Coleman, Harris 1996; Fox et al. 2010; Liu et al. 2010). GR depended upon the number of live, germinant seeds per unit weight (Karaguzel et al. 2004; Hossain et al. 2005). The prevalent seed mix established lower percent grass cover and had a slower GR than the hydroseed mixes. So, based on this result it is not recommended to use this mix for artificial slope stabilization practice. It was con-firmed that hydroseed mix 2 provided favourable soil moisture and temperatures for grass seeds and this accelerated the plant establishment.

Biomass production of grass

to-tal dry weight of grass, with higher values in hy-droseed mix 2 than in the other two treatments. At this time, the average of total lengths for three slope classes was 11.7 and 15.7 cm in the plots of hydroseed mix 1 and 2, and 8.5 cm in the prevalent mix plots, respectively. Vitality ranged from 73.8 to 74.4% in hydroseed mix 2 (Table 4). Root length and biomass in plots treated with hydroseed mix 2 were significantly higher than in the other treatments. Numerous long grass roots growing almost verti-cally downwards are able to penetrate and mitigate the soil erosion (Mickovski, van Beek 2009).

Water requirement of treatments

A higher volume of total and daily irrigation wa-ter was found on the prevalent mix plots. There was also a higher volume of irrigation water found on the higher slope angle plots. The hydroseed mix 1 and 2 treatments were observed to be the most effective in terms of irrigation water volume with 12.8 and 16.5% reduction, respectively, as com-pared to the prevalent mix treatment (Table 5). A superabsorbent in hydroseed mix controlled the ir-rigation requirement of grass.

Table 2. Analysis of variance showing the effect of the different treatments on germination, biomass and irrigation of grass and soil erosion from the plots

Source of variation _SSTreatment type_MS F-value _SSSlope treatment_MS F-value Germination

Final germination 10,336.9 5,168.4 34.8*** 552.7 276.3 1.9

Mean daily germination 12.4 6.2 27.4*** 1.5 0.8 4.4*

Germination rate 51,490.8 25,745.4 30.1*** 4,080.1 2,040.1 2.4

Germination index 91.7 45.8 38.9*** 2.0 1.0 0.9

Biomass production

Leaf length 38.2 19.1 35.5*** 3.2 1.6 2.9

Root length 84.6 42.3 117.0*** 4.3 2.1 5.9**

Total length 232.2 116.1 81.8*** 12.5 6.3 4.4*

Leaf fresh weight 98.8 49.4 7.3** 52.4 26.2 3.9*

Root fresh weight 35.6 17.8 6.9** 21.9 10.9 4.2*

Total fresh weight 251.1 125.5 7.6** 138.7 69.3 4.2*

Leaf dry weight 3.7 1.8 9.5** 1.2 0.6 3.0

Root dry weight 3.7 1.8 7.0** 1.2 0.6 2.3

Total dry weight 14.8 7.4 10.2** 4.2 2.1 2.9

Vitality 7,455.1 3,727.6 7.3** 442.5 221.2 0.4

Irrigation

Mean daily irrigation 22,412.7 11,206.4 126.6*** 35.2 17.6 0.1

Total irrigation 2.02 1.01 126.5*** 31,666 15,833 0.2

SS – sum of squares, MS – mean of squares, ***significant at P = 0.001, **significant at P = 0.01, *significant at P = 0.05, without sign – not significant

Table 3. Effect of the different slope treatments on germination parameters of grass (mean ± standard error)

Slope (°) Treatment FG (%) MDG GR GI

20 hydroseed mix 1 67.55 ± 7.70

b _{2.37 ± 0.23}b _{141.32 ± 11.56}b _{6.86 ± 1.05}b hydroseed mix 2 86.88 ± 9.42a _{3.33 ± 0.35}a _{201.92 ± 22.45}a _{7.60 ± 1.75}a prevalent mix 30.78 ± 0.83c _{1.06 ± 0.07}c _{62.99 ± 3.64}c _{3.22 ± 0.05}c

45 hydroseed mix 1 63.08 ± 0.37

a _{2.10 ± 0.01}a _{131.15 ± 1.29}a _{6.48 ± 0.03}a hydroseed mix 2 66.45 ± 5.60a _{2.22 ± 0.19}a _{140.79 ± 11.45}a _{6.67 ± 0.57}a prevalent mix 23.03 ± 6.33b _{0.77 ± 0.21}b _{47.02 ± 14.88}b _{2.46 ± 0.56}b

70 hydroseed mix 1 61.13 ± 4.13

a _{2.04 ± 0.14}a _{132.30 ± 8.80}a _{6.00 ± 0.44}a hydroseed mix 2 66.03 ± 6.33a _{2.20 ± 0.21}a _{134.81 ± 14.88}a _{6.55 ± 0.56}a prevalent mix 16.18 ± 4.23b _{0.60 ± 0.13}b _{31.50 ± 9.31}b _{1.78 ± 0.42}b

CONCLUSIONS

This study explored the effectiveness of three soil stabilization treatments. A new proposed treat-ment was the use of hydroseed mix 2 as a mulch-based treatment. Hydroseed mix 2 was clearly much more efficient than hydroseed mix 1 and prevalent seeding in terms of grass germination, vegetation biomass and irrigation level. Cellulose fibre mulch, organic tackifier and superabsorbent in hydroseed mix 2 provided a hydrogel layer dur-ing the study time that was the reason for 16.5% reduction in irrigation requirement. The hydrogel layer can reserve water in its structure and con-sume water during the day. In addition, starter fer-tilizer and biohumus in hydroseed mix 2 contain fortified amino acids, gibberellic acid and micro-elements which can accelerate seed germination and produce more grass biomass. We found that

the average germination index and biomass in all of the slope classes increased to 6.94 and 27.77 g·m–2_, respectively, when hydroseed mix 2 was used. From the management point of view, our results support the use of hydroseed mix 2 as an efficient bioengi-neering alternative to stabilize hillslopes after for-est road construction.

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20 hydroseed mix 1 348.33 ± 173.54

b _10,450.00 hydroseed mix 2 343.33 ± 163.33b _10,300.00 prevalent mix 405.00 ± 146.34a _12,150.00

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Slope

(°) Treatment (cm)LL (cm)RL (cm)TL (g·mLFW –2_{) (g·m}LDW –2₎ RFW _{(g) (g·m}RDW –2_{) (g·m}TFW –2_{) (g·m}TDW –2_{) (%)}V

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45 hydroseed mix 1 6.5

b _5.0b _11.5b _49.7b _17.9a _13.5b _8.5b _63.2b _26.4a _58.3b

hydroseed mix 2 8.5a _7.2a _15.7a _54.2a _12.2b _34.2a _11.7a _88.4a _23.8a _73.0a prevalent 6.0b _2.7c _8.7c _8.3c _4.4c _6.2c _4.9c _14.5c _9.2b _36.2c

70 hydroseed mix 1 6.5

a _4.0b _10.5b _22.3b _7.6b _17.7b _8.3b _39.9b _15.9b _60.1b

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